Oxidation of alkyl-substituted cyclohexanes using aldehydeactivated catalysts



Patented Mar. 11, 1952 OXIDATION OF ALKYL-SUBSTITUTED CYCLOHEXANES USINGALDEHYDE- ACTIVATED CATALYSTS David 0. Hull, Kingsport, Tenn., assignorto Eastman Kodak Company, Rochester, N. Y., a corporation of New JerseyApplication December 16, 1949, Serial N 0. 133,341 h 7 Claims.

This invention relates to the liquid phase catalytic oxidation ofsubstituted cyclohexanes to obtain cyclic acids and ketones and moreparticularly to the oxidation, by means of aldehydeactivated metalcatalysts, of alkyl-substituted cyclohexanes to form cyclic acids underconditions in which ring cleavage is avoided.

For many years in the carrying out of oxidations such as the conversionof various aliphatic alcohols to the corresponding acids it wasnecessary to employ a roundabout and indirect procedure involving amultiplicity of steps and complicated apparatus. For example, in theconversion of ethyl alcohol to acetic acid it was the practice first tooxidize the alcohol to acetaldehyde in one step and then, by a separatestep, to oxidize the aldehyde to the acid. In later years a greatlyimproved and far more economical technique has been developed, wherebythe alcohol may be converted directly, at relatively low temperature andpressure, into the corresponding acid without the necessity of aseparate procedure for first obtaining the aldehyde. For example, in myUnited States Patents Nos. 2,287,- 803; 2,353,157; 2,353,158; 2,353,159;2,353,160; 2,425,878; 2,425,879; 2,425,880; 2,425,881; 2,425,- 882, Ihave described an improved process wherein an alcohol, such as ethylalcohol, may be converted directly to acetic acid by oxidizing thealcohol in the liquid phase by means of oxygen or an oxygen-containinggas in the presence of certain metal catalysts dissolved in an aliphaticacid and maintained in an active state through the agency of acontinuous supply of aldehyde. This process has proved to be extremelyelfective and economical for the production of aliphatic acids.

The catalytic oxidation of other organic compounds employing a somewhatsimilar technique, although operated, in general, under conditions whichdiffer substantially from the low temperature processes described in myabove-mentioned patents, has been applied to various aliphatic,alicyclic and aromatic ketones, including acetone, methyl ethyl ketone,cyclohexanone, methyl cyclohexanone and acetophenone to convert them tomonobasic and dibasic acids such as acetic, propionic, adipic, methyladipic and benzoic acids. Such a process is described in Flemming et a1.2,005,183.

In Patent 2,223,493 Loder has described the liquid phase catalyticoxidation of cyclic saturated hydrocarbons such as cyclohexane,cyclopentane, cyclobutane and their substituted derivatives to obtainthe corresponding aliphatic dibasic acids, such as adipic, glutaric andsuccinic. In Patent 2,223,494 Loder describes a similar process forconverting cyclic saturated hydrocarbons to cyclic alcohols and ketones,while in Patent 2,265,948 he describes a process involv ing conversionof open chain aliphatic hydrocarbons to acids, ketones, esters andalcohols.

A further extension of the broad concept of oxidizing organic compoundsin the liquid phase is described by Loder in Patent 2,245,528 in whichreference is made to the oxidation of alkyl-substituted aromaticcompounds such as ethyl benzene, toluene and the xylenes to thecorresponding aromatic acids such as benzoic, toluic, phthalic and thelike. A similar but more specific process is disclosed in the patent toHenke 2,276,774.

Reference to these patents will disclose that in no case have any of thevarious workers in this field conceived that the alkyl-substitutedcyclohexanes could be converted to the corresponding cyclic acids orketones without cleavage of the carbon ring. Furthermore, not only havenone of these researchers recognized or applied the principle ofaldehyde activation to such oxidations, but they also have operatedunder relatively high temperature conditions and obtained relatively lowyields of theirrespective products.

The present invention has for its principal object to provide a processfor the economical and eflicient conversion of alkyl-substitutedcyclohexanes to form cyclic acids and cyclic ketones. A further objectis to provide a process whereby such compounds may be directly oxidizedto the desired products without cleavage of the alicyclic ring and theresulting production of substantial amounts of open chain acids or otheraliphatic compounds. A still further object is to provide a processwhereby such oxidations may be carried out in a single step. Anotherobject is to provide a process for the direct oxidation of thealkyl-substituted cyclohexanes to saturated cyclic acids and cyclicketones in high yields at relatively low temperatures at either ordinaryatmospheric or superatmospheric pressure conditions. Other objects willappear hereinafter.

These objects are accomplished by the following invention which, in itsbroader aspects, comprises firstpreparing an active catalyst solution bydissolving an appropriate metal, metal oxide or other suitable metalcompound in an aliphatic acid, such as acetic acid, treating thesolution with an oxygen-containing gas and simultaneously adding analdehyde such as acetaldehyde,

thereby to bring the metal catalyst into a highly active state, andthereafter feeding the desired alkyl-substituted cyclohexane, togetherwith an excess of oxygen, into the catalyst solution while maintainingthe catalyst in the solution in an active state by continuously addingaldehyde. In accordance with the invention the solution is maintainedunder such conditions of temperature and pressure that the solution ismaintained in the liquid phase and the cyclic compound in the solutionis directly converted to the corresponding cyclic acid. For example, bymaintaining a body of active catalyst solution in an appropriate vesselat a temperature within the range of C. and 90 C. and approximatelyatmospheric pressure and continuously adding methyl cyclohexane,acetaldehyde and oxygen or air to the solution, I obtain substantialyields of cyclohexanoic acid (hexahydrobenzoic acid).

In the following examples and description, I have set' forth severalhfth'e preferred embodiments of my inventionjbutthey are included merelyfor purpos illustration and not as a limitation thereof,

The single figure oi the drawing represents one form of apparatus"may'rie employed for the practice of my inven Qther suitable forms ofapparatus which"'rnay be employed for the carrying out of such aprcicess are illustrated in my abovementioned patents for example, Pat- Ients 2,287,803 and 2,353,157.

My invention will be more fully understood by a preliminary discussionof the preparation and the composition of my improved catalyst solutionsand the general conditions under which my process is operated.

AS indicated, I employ what I have described as an aldehyde-activatedmetal catalyst solution. Sucha solution can appropriately be prepared,by dissolving a suitable catalyst metal or one of its aliphaticacid-soluble oxides, salts or other compound in an aliphatic 'acid suchas acetic, propionic or butyric acid. While in accordance with myinvention, I may employv almostrany metal which will produce metallicions in solution, I

have found cobalt to be 'an especially valuable.

catalyst. In the same class with cobalt may be mentioned manganese;iron, nickel and, copper. Gther metals which may be, employed as,catalyst with substantially equa facility are lithium,

beryllium, sodium, potassium, rubidium, caseium, calciumfstrontium,barium, magnesium, zinc, aluminum, scandium, yttrium, lanthanum,neoytteibium, gallium, indium, thallium, cerium, ruthenium, rhodium,palladium, osmium, iridium, platinum, gold, tin, antimony, mercury,lead, chromium, .molybdenum, tungsten, uranium, tantalum, vanadium,columbium, niobium, ti-

tanium, thorium, neodymium, praseodymium, il-

linium, samarium, holmium, europium, erbium, gadolinium, thulium,terbium, dysprosium, and

luteciuin.

While in general I prefer to employ. a single metal as the catalyst andin, the form of one of its oxides, salts or other compound which iseasily soluble in the aliphatic acid selected as the solvent medium, Imay, if desired, employ a plurality of such metals. For example, while Iprefer to employ a solution of cobaltous acetate. C0(C2H3 O2)2.4H2 O inglacial acetic acid, I may employ a plurality of metals in the form oftheir. acetates, propionates or butyrates, or in the form of oxideswhichform' thef'corresponding aliphatic acid salts in the acid'solution.Likewise, while Iprefer to use acetic acid alone as the solvent,

I may employ aliphatic acids such as acetic, propicnic, butyric and thelike, either singly or in various combinations one with another.

As to the matter of concentration, I may dissolve the catalyst metal inthe acid to produce solutions containing anywhere from 0.1% to 8% of themetal, although, in general, I prefer to keep within the range of 5% to8%. Likewise, although I prefer to dissolve the catalyst in anhydrousacid, a more dilute acid may be employed. In general, I have found that,in use, more satisfactory. yields of product are obtained if the acidconcentration of the catalyst solution is at all times maintained atapproximately Once the catalyst solution has been prepared as abovedescribed and charged into a suitable reaction vessel, it is broughtinto a highly active or activated condition by simultaneously feeding inan aliphatic aldehyde, such as acetaldehyde, and oxygen oranoxygencontaining gas at such a rate and at such atemperature as tocause the catalyst to become and remain active, a condition usuallyinitially indicated by change in color of the original solution. Theoxyn f d is late to provide a slight excess r oxygen over and above thatrequired for the oxidation reaction, such excess being indicated by thepresence of a few per cent of oxygen in the gaseous eflluents from theprocess. It will, of course, be understood that such matters as feedrates of aldehyde and oxygen, temperature and the like, in general, haveto be determined for each particular catalyst and with reference to thecompound to be oxidized. In the case of a cobalt catalyst in aceticacid, the original solution, which is pink, changes to green uponactivation, indicating that the cobalt ions have changed from a lower toa higher state of valence, that is, from the cobaltous to the cobalticstateand that the solution is in the desired catalytically activecondition. While air is the most economical source of oxygen, I mayemploy any suitable oxygen-contain: ing gas such as pure oxygen, ozone,or mixtures of such gases with inert gaseous diluents. Likes wise,although I prefer to use acetaldehyde, I may employ other aliphaticaldehydes suchaspropionaldehyde, butyraldehyde and the like, all orwhich aldehydes may be employedsingly or. in various combinations. onewith another. In, gen eral, the aldehyde feed will be so regulatedas tomaintain 1% to 5% of the aldehyde in the reaction liquid. I

While in some cases the catalyst solution will become active merely uponintroduction of the aldehyde and blowing with air or oxygen at ordi naryatmospheric temperatures, it may be necessary to heat the solutionmoderately, say, to a temperature in the vicinity of 50-60 C. in order,to initiate catalyst activity.

As to the matter of temperature, I may oxidize alkyl-substitutedcyclohexanes in accordancewith my invention at a temperature within therange of 5 C. to 150 0., although I prefer to operate in the vicinity of80 C. to C. In general, high temperatures, that is, temperatures inexcess of the boiling point of the solvent or product, are to be avoidedin the interest offpre-j eluding degradation of reactants or products,or losses by evaporation, polymerization or like phenomena. In view ofthe fact thatthe oxida-, tion reactions here involved are exothermic incharacter, it is usually necessary continuously to cool the reactionmedium in order to keepthe temperature within the desired limits, toprevent J excessive loss of reactants by evaporation and to preclude thepossibility of the reaction becoming too greatly accelerated. On theother hand, under certain circumstances it may be necessary actually tosupply heat, as, for example, in the case of first starting the process,in order to initiate catalyst, activity.

As to pressure, while I prefer to operate at atmospheric pressure, I mayoperate at pressures below atmospheric or as high as 2 to 10 atmospheresor more. pheric in general permit operation at higher temperatures. Itwill of course be understood that thetemperature and pressure will varyaccording to the requirements of the particular material undergoingoxidation, the rate of feed of the several reactants and with othervariables, the control of which is within the skill of the trainedchemist or chemical engineer.

It will, of course, be understood that in oxidizing alkyl-substitutedcyclic hexanes in accordance with my invention the oxygen supplied bycontinuous introduction of air or other oxygen-containing gas, asexplained above, is the fundamental source of oxygen for the oxidationreaction. The chief reaction product will be one or more of thecyclohexanoic acids or homologous or related acids. For example, methylcyclohexane yields cyclohexanoic acid, ethyl cyclohexane gives methylcyclohexyl ketone and cyclohexanoic acid, 1,4 dimethyl cyclohexaneconverts to hexahydroterphthalic acid, and so on, together with theproduction of small amounts of carbon dioxide, formic acid and otherdegradation products.

My invention will now be more clearly understood by reference to apractical operation which may be conveniently carried out in anapparatus such as that illustrated in the single figure of the drawing.

The numeral I designates an oxidation unit which may consist of aplurality of flanged stainless steel tubes of six-inch inside diameterand approximately ten feet long, or any other convenient size orproportions, superimposed one on top of the other and bolted together,the main sections being represented by numerals 2, 3, 4 and 5. Eachsection is provided with a suitable cooling means which may take theform of an in-' ternal centrally disposed stainless steel coil, such ascoil 6 of section 5, of one-half inch or other appropriate insidediameter, each coil being supplied with cooling medium, such as waterthrough inlet 1 and emerging therefrom through outlet 8. Each section isalso supplied with a thermometer, as shown, inserted through the wall ofeach section by means of a thermometer well (not shown) The lowermostsection of the oxidation unit consists of a tubular stainless steelmember 9 of the same inside diameter as the upper sections of the unit,flanged at the top and closed at the bottom. To section 9 is connectedinlet conduit, l0, flow of liquid through which is controlled by valveH. Connected into conduit I is valved aldehyde feed conduit l 2 andanother valved conduit l3 for supplying the material to be oxidized tothe oxidation unit. While the valves in these feed lines may be sooperated as to provide a regulated or metered flow of materials to theunit, a, somewhat more convenient method is to provide rotameters orother metering device's 'for this purpose.

Section 9 has tapped into its lower closed end another inlet conduit l4into which is connected air inlet conduit l5, flow of air or otheroxygen Use of pressures above atmos-- means for draining the unit whennot in use or between successive runs.

A perforated difiusion plate is inserted and bolted in place between thelower flange of section 2 and the flanged top of bottom section 9 toprovide a means of evenly distributing the liquidgaseous mixture whichenters the bottom of the unit.

The topmost portion of the oxidation unit may conveniently comprisethree sections, l8, l9 and 20, each of which is flanged and boltedtogether as previously described. A distributor plate, which may includea bubble cup and downcomer, is positioned between the upper flange ofsection 5 and the lower flange of section I8. To sections l8 and I9there is connected a high-pressure sight glass 2| for indicating thelevel of liquid in the upper part of the unit.

The upper closed end of section 2B is provided with an outlet conduit 22adapted to conduct vapors and gas evolved from the top of the unit tocyclone separator 23 where any entrained liquid is separated from themixture and conveyed back into the upper part of the oxidation unit atsection I8 through conduit 24, the latter being so formed at its end asto provide a liquid seal in proximity to its junction with section I8.

Cyclone separator 23 is also provided with an outlet conduit 25 whichconveys gaseous and vaporous materials to water-cooled condenser 26 ofappropriate size and design, cooling medium for which is suppliedthrough inlet 21 and emerges through outlet 28. Condenser 26 i alsoconnected through conduit 29 and sight glass 30 to product receiver 3|,the latter also being provided with a sight glass 32 for indicating thelevel therein.' The product receiver is also equipped with valvedconduit 33 for withdrawing product therefrom as desired.

Vapors not condensed in condenser 25 may find their way in the directionindicated by the arrows, through conduits 3t, 35, and 36 into the bottomof scrubber 31 which may take the form of a stainless steel tube ofappropriate diameter packed with a liquid distributing material such asberl saddles or Raschig rings. Scrubber 31 is provided near its upperclosed end with conduit 38 through which water is supplied, passing incountercurrent to the vapor-gas stream ascending in 3'! and therebydissolving out any portions of products or reactants which may haveescaped entrapment in separator 23 or condenser 25.

The lower end of scrubber at is connected, through conduit se' toreceiver 3!. The scrubber receiver may be drained, when necessary,through valve 33" to a recovery system.

Scrubber 31 is also provided at its upper end with a gas outlet conduit37 and pressure con-' trol valve 39. The gas then escapes throughpressure control valve 39 to the atmosphere.

In order to recover the acid made from the oxidation of thealkyl-substituted cyclohexanes, the catalyst solution is withdrawn fromthe oxidation unit at a slow rate through conduit 39, valves 40 or 4| tojacketed crystallizers 4d or 45. Cooling medium isturned into thejackets of the crystallizers and the mixture is cooled to around 5 C.While crystallization is being carried out in one crystallizer, theother is being filled. When thecrystallization is complete valve 44 C51-45{ opened and the material is allowed to pass into filter 46 or to acentrifuge. The solid acid is removed from the filter or centrifuge andfurther purified. The filtrate, containing most of catalyst passesthrough conduit 49 to receiver 50 or From here it is pumped continuouslyby means of pump 53 to the oxidation unit.

The oxidation unit is operated at such a temperature that the acidproduced is boiled ofi through conduit 22, through separator 23 andcondenser 26 to receiver 3|, as it is made.

The operation of the apparatus when used to carry out the process of myinvention will be apparent on inspection. in starting, oxidation unit 4is filled somewhat less than full with catalyst solution, which mayconventiently take the form of a 3% solution of cobaltous acetate inglacial acetic acid. Air valve I6 is opened slightly and aldehyde feedis put on the unit by opening the valve in feed line I2. It will, ofcourse, be understood that a suitable cooling medium such as water issupplied to the several coils of the unit and that the thermometers arein place in the respective thermometer wells for taking readings of thetemperature of the solution.

If the catalyst solution does not become active, as indicated by changein color from pink to green, after the elapse of several hours, it maybe necessary to supply steam to the coils instead of cooling medium,thus to raise the temperature to approximately 60 C. When the catalysthas become active, it is generally desirable to add more cobalt acetateto bring the concentration up to approximately 6%. The amount ofcatalyst dissolved in the original solution will vary, not only with theparticular catalyst selected, but also with the temperature and variousother conditions. Sufiice it to say that a few percent of the materialis generally sur'hcient for effective operation.

Once the catalst has been activated, the material to be oxidized isintroduced into the oxidation unit through conduit I3 and the aldehydeand air feeds are adjusted so as to provide the proper proportion ofeach material to perform their respective functions. In general, therate of aldehyde introduction will be controlled so as to maintain thecatalyst at all times in an active condition, while the rate of oxygenfeed will be so regulated as to provide a slight excess of oxygen overand above that actually required for oxidation of the material beingconverted, as indicated by a few percent of free oxygen in the effluents from the process.

Assuming the material to be oxidized, and aldehyde and air or oxygen,are being continuously fed, oxidation product will be continuouslyremoved from the unit through conduit 22 and conduit 39. A certainamount of gaseous and liquid material also passes out of the devicealong with the product, the liquid portions being separated from theaseous or vaporous portions in cyclone separator 23 and eventuallyreturned to the zone of oxidation through conduit 2 3.

The major portion of the condensable vapors, consisting mainly of theproducts of oxidation, are condensed in condenser 26 and find their wayinto product receiver 3| from which they are continuously removed atsuch a volume rate as to maintain the proper liquid level in theoxidation unit. The uncondensable gases and vapors are conveyed throughconduits 3t, 35 and 36 into water scrubber 31, passing upwardly incountercurrent to a stream of water. Any vaporized materials which haveescaped condensation in condenser 26 are thus dissolved in the water andpass to receiver 3 I.

The product of the process may be removed from the system and conveyedto any desired concentrating or purifying steps for conversion into thedesired concentrated acid or other product. Likewise, the acid or othermaterials which have been scrubbed out of the vapor-gas stream passingthrough scrubber 31 may be removed from scrub receiver 3! through valvedconduit 33 and treated in any appropriate manner for recovery of thedissolved materials.

As'to the matter of temperature, I may conveniently carry out oxidationsin accordance with my process, when operated at atmospheric pressure,within the range of -5 C. to C. Since the reactions involved areexothermic, it is generally necessary continuously to supply a coolingmedium to the coils of the oxidation unit in order to maintain thetemperature within the indicated limits. However, in some cases, as forex.- ample, in oxidizing materials of high boiling points, or inaccelerating the oxidation reaction, it may be desired to employ highertemperatures than those indicated. When such higher temperatures areemployed, pressures in excess of atmospheric will be desirable in orderto prevent boiling away, either of the acetic or other aliphatic acidcatalyst solvent or of the product of the reaction itself. Whenemploying apparatus such as described herein for the carrying out ofoxidation reactions at higher temperatures, say in the range of C. to150 C., it will be understood that valve 38' will be closed andprovision made for maintaining the desired pressure in the system.Pressure operation will of course require that reactants and scrubbingmedia be in.- troduced under a pressure sufficient to compensate orbalance the pressure existing in the system. While the pressure mayunder such circumstances vary over a wide range, depending on thetemperature it is desired to maintain in the oxidation Zone and onvarious other factors, in general pressures ranging from atmospheric to10 atmospheres are satisfactory.

My invention will be more fully understood by reference to a number ofspecific examples illustrating typical conversions carried out inaccordance therewith.

EXAMPLE I Oxidation of methyl cyclo errane to cyclohexs anoic acid Theoxidation unit was filled approximately /3 full with a catalyst solutionwhich comprised about 3% cobalt acetate in glacial acetic acid. Air wasturned on and acetaldehyde feed was started. The initial temperature was30? C. and after two hours the temperature rose rapidly to 60 C. atwhich time cooling water was added to maintain the temperature at (SO-70C. Morelcobalt acetate was added to bring the content up from 3 to 6%.After severalhours operation with the additional cobalt acetate added,the catalyst solution was sufficiently active to start full operation.

The feed was adjusted at such a rate so that 20 mol per cent methylcyclohexane and 80 mol per cent acetaldehyde was being fed. Thetemperature was controlled at 70-80 C. at atmospheric pressure. The feedwas continuousat the rate of 29 units of methyl cyclohexane per hour and53' units of acetaldehyde per hour. At the end of ten hours operation itwas found that units of cyclohexanoic acid were made, representlng a 35%conversion per pass. The ultimate yield based on methyl cyclohexane was91%. The cyclohexanoic acid was removed from the system continuously bywithdrawing the catalyst solution, containing the dissolvedcyclohexanoic acid, into a cooled tank. The solution was cooled to about(3., and a good portion of the cyclohexanoic acid crystallized out. Thecrystals were then filtered out or centrifuged and purified. Thefiltrate, which contained most of the catalyst was then returned to theoxidation unit. The filtrate also contained unconverted methylcyclohexane in an amount corresponding to 65% unconverted methylcyclohexane.

EXAMPLE II Oxidation of ethyl cyclohexane to cyclohexanoz'c acid andmethyl cyclo eccyl Icetone A catalyst was prepared in a similar manneras described in Example I. In this case ethyl cyclohexane andacetaldehyde were fed continuously to the oxidation unit in the ratio of20 mol per cent to 80 mol per cent. The temperature was maintained at70-80 C. and the pressure atmospheric. After feeding a total of 370units of ethyl cyclohexane and 580 units of acetaldehyde', it was foundthat 127 units of cyclohexanoic acid was made and small amounts ofmethyl cyclohexyl ketone representing a conversion of ethyl cyclohexaneto cyclohexanoic acid of 30% per pass and of ethyl cyclohexane to methylcyclohexyl ketone of approximately 3%. The ultimate yield based on ethylcyclohexane was 89%. The recovery of the acid and the recycling of thecatalyst was carried out in the same manner as described in Example I.

EXAMPLE III Om'dation of 1,4 dimethyl cyclohexane tohexahydroterphthalic acid After preparing an active catalyst as inExample I, 1,4 dimethyl cyclohexane was fed to the cyclohexane and 89mol per cent acetaldehyde or a total of 168 units of 1,4 dimethylcyclohexane and 530 units of acetaldehyde over a 10 hour period. Aftercompleting the run,

acid was made, representing a conversion of 25% of 1,4 dimethylcyclohexane to the acid per pass.

An ultimate yield of 90.5% was obtained based on the 1,4 dimethylcyclohexane fed. The recovery of the acid and the recycling of thecatalyst was done as described in Examples I and 11.

What I claim is:

1. A process for the direct and the substantially continuous oxidationof methyl cyclohexane to cyclohexanoic acid wherein a predeterminednumber of units of the methyl cyclohexane per hour are subjected to thesubstantially continuous oxidation process which comprises preparing acobalt acetate catalyst solution in acetic acid by incorporatingapproximately 3% cobalt acetate in glacial acetic acid, activating thiscatalyst solution by passing air and acetaldehyde therethrough at atemperature between 30-60 0., adding further cobalt acetate to thecatalyst solution to bring the content of the cobalt up to approximately6%, continuing the treatment of the catalyst solution with air andacetaldehyde for several hours until the catalyst solution is activated,then passing into the activated catalyst solution the methylcycleoxidation unit along with acetaldehyde. The ratio of feed was 11mol per cent 1,4 dimethyl analysis showed that 64.5 units of hexahydroterphthalic hexane wherein a predetermined number of units thereof perhour are substantially continuously oxidized to cyclohexanoic acid whichcomprises preparing an acetic acid catalyst solution by incorporating ametal ion in glacial acetic acid, activating this catalyst solution bypassing air and acetaldehyde therethrough at a temperature between30-60" (3., adding further metal ion to the catalyst solution,continuing the treatment of the catalyst solution with air andacetaldehyde for several hours until the catalyst solu tion is fullyactivated, then passing into the activated catalyst solution the methylcyclohexane to be oxidized, additional acetaldehyde for maintaining theactivity of the catalyst and gaseous oxidizing medium, the process beingcharacterized in that the units per hour of acetaldehyde substantiallycontinuously fed to the process are substantially in excess of the unitsper hour of cyclohexane substantially continuously fed,

-maintaining the process under a temperature lyst solution byincorporating a metal ion in a lower aliphatic acid, activating thiscatalyst solution by passing air and acetaldehyde therethrough at atemperature between 30-60" C., adding further metal ion to the catalystsolution, continuing the treatmentof the catalyst solution with air andaldehyde for several hours until the catalyst solution is activated,then passing into the activated catalyst solution the ethyl cyclohexaneto be oxidized, additional aldehyde for maintaining the activity of thecatalyst and gaseousoxidizing medium, the process being characterized inthat the units per hour of aldehyde fed substantially continuously tothe process are substantially in excess of the units per hour oftheethyl cyclohexane continuously fed, maintaining the process under atemperature between -5 and C. and at a pressure such that a substantialportion of catalyst solution is maintained in liquid phase, thereafterrecovering the aforesaid products produced.

4. A process for the direct oxidation of 1,4 dimethyl cyclohexane tohexahydroterphthalic acid which comprises preparing a catalyst solution,

hour of aldehyde fed to the process are substantially in excess of theunits per hour of the 1,4 dimethyl cyclohexane continuously fed,maintaining the process under a temperature between -5 and 90 C. and ata pressure such that the solution is maintained in liquid phase, andthereafter recovering the hexahydroterphthalic acid produced. 1

5. A process for the direct oxidation of alkylsubstituted cyclohexanesfrom the group consisting of methyl cyclohexane, ethyl cyclohexane anddimethyl cyclohexane by procedure including substantially continuouslyoxidizing a predetermined number of units per hour of the substitutedcyclohexanes to a cyclic carboxylic acid which comprises preparing anactivated catalyst solution, then substantially continuously passingthrough this activated catalyst solution the substituted cyclohexane tobe oxidized and also substantially, simultaneously and continuouslypassing through the activated catalyst solution, additional amounts of alower aliphatic aldehyde and gaseous oxidizing medium, the units of thealdehyde passed through the activated catalyst solution substantiallyexceeding the units of the substituted cyclohexane per hour passedthrough the solution, maintaining the catalyst solution during theprocess at a temperature within the range of -5 C. and 90 C. and apressure such that the substantial part of the catalyst solution remainsin the liquid phase and recovering the cyclo carboxylic acid produced.

6. A process for the direct oxidation of alkylsubstituted cyclohexanesfrom the group consisting of r ethyl cyclohexane, ethyl cyclohexane anddimethvl cyclohexane by procedure including substantially continuouslyoxidizing a predetermined number of units per hour of the substitutedcyclohexanes to a cyclic carboxylic acid which comprises preparing anactivated catalyst solution, by substantially continuously treating thecatalyst solution for several hours with a gaseous medium comprised ofair and lower aliphatic aldeh de whereby the catalyst solution isactivated, then substantially continuously passcyclic carboxylic acidproduced by substantially continuously withdrawing from the oxidationprocess catalyst liquid containing the acid, subjecting the Withdrawnliquid to a crystallization treatment whereby crystals in the withdrawncatalyst liquid are formed, separating the cyclic acid crystals from theliquid, returning the catalyst liquid to the oxidation process and priorto the introduction of the catalyst liquid into the oxidation processincorporating a content of lower aliphatic acid therein.

'7, A process for the direct oxidation of alkylsubstituted cyclohexanesfrom the group consisting of methyl cyclohexane, ethyl cyclohexane anddimethyl cyclohexane by procedure including substantially continuouslyoxidizing a predetermined number of units per hour of the cyclohexanesto a cyclic carboxylic acid which comprises preparing an activatedcatalyst solution by substantially continuously for several hourstreating cobalt acetate in acetic acid with a gaseous medium whereby thecatalyst solution is activated, said gaseous medium comprised of a loweraliphatic aldehyde and air, then substantially continuously passingthrough this activated catalyst solution the substituted cyclohexane tobe oxidized and also substantially, simultaneously and continuouslypassing through the activated catalyst solution additional amounts of alower aliphatic aldehyde and gaseous oxidizing medium, the units of thealdehyde passed through the activated catalyst solution exceeding theunits of the substituted cyclohexane per hour passed through thesolution, maintaining the catalyst solution during the process at atemper-- ature within the range of -5 and 90 C. and a pressure such thatthe substantial part of the catalyst solution remains in the liquid phae and recovering the cyclic acid produced by substantially continuouslywithdrawing from the oxidation process catalyst liquid containing theacid, subjecting the withdrawn liquid to a crystallization treatmentwhereby crystals in the withdrawn catalyst liquid are formed. separatingthe cyclic acid crystals from the liquid and returning the catalystliquid to the oxidation process.

DAVID C. HULL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,223,493 Loder Dec. 3, 19402,245,528 Loder June 10, 1941 2,276,774 Henke Mar. 17, 1942 2,302,463Palmer et al Nov. 17, 1942

1. A PROCESS FOR THE DIRECT AND THE SUBSTANTIALLY CONTINUOUS OXIDATIONOF METHYL CYCLOHEXANE TO CYCLOHANOIC ACID WHEREIN A PREDETERMINED NUMBEROF UNITS OF THE METHYL CYCLOHEXANE PER HOUR ARE SUBJECTED TO THESUBSTANTIALLY CONTINUOUS OXIDATION PROCESS WHICH COMPRISES PREPARING ACOBALT ACETATE CATALYST SOLUTION IN ACETIC ACID BY INCORPORATINGAPPROXIMATELY 3% COBALT ACETATE IN GLACIAL ACETIC ACID, ACTIVATING THISCATALYST SOLUTION BY PASSING AIR AND ACETALDEHYDE THERETHROUGH AT ATEMPERATURE BETWEEN 30-60* C., ADDING FURTHER COBALT ACETATE TO THECATALYST SOLUTION TO BRING THE CONTENT OF THE COBALT UP TO APPROXIMATELY6%, CONTINUING THE TREATMENT OF THE CATALYST SOLUTION WITH AIR ANDACETALDEHYDE FOR SEVERAL HOURS UNTIL THE CATALYST SOLUTION IS ACTIVATED,THEN PASSING INTO THE ACTIVATED CATALYST SOLUTION THE METHYL CYCLOHEXANETO BE OXIDIZED, ADDITIONAL ACETALDEHYDE FOR MAINTAINING THE ACTIVITY OFTHE CATALYST AND GASEOUS OXIDIZING MEDIUM, THE PROCESS BEINGCHARACTERIZED IN THAT THE UNITS PER HOURS OF ACETALDEHYDE FED TO THECONTINUOUS OXIDATION PROCESS ARE SUBSTANTIALLY IN EXCESS OF THE UNITSPER HOUR METHYL CYCLOHEXANE CONTINUOUSLY FED, MAINTAINING THE PROCESSUNDER A TEMPERATURE BETWEEN -5* AND 90* C. AND AT A PRESSURE SUCH THAT ASUBSTANTIAL PART OF THE SOLUTION IS MAINTAINED IN LIQUID PHASE,THEREAFTER RECOVERING THE CYCLOHEDXANOIC ACID PRODUCED.